1. Field of the Invention
This invention relates to a light converging sheet unit, more particularly to a light converging sheet unit capable of converging light and reducing Newton-rings.
2. Description of the Related Art
Generally, a conventional backlight module for a liquid crystal display (LCD) includes a light source, a light guide plate that is disposed above the light source, a lower diffusion sheet that is disposed above the light guide plate, first and second light converging sheets that are stacked one on top of the other, that are disposed above the lower diffusion sheet, and that respectively have micro-prism structures, and an upper diffusion sheet that is disposed above the first and second light converging sheets. The micro-prism structures of the first light converging sheet extend in a first direction, and the micro-prism structures of the second light converging sheet extend in a second direction approximately transverse to the first direction. Accordingly, the first and second light converging sheets cooperate to converge light in both of the first and second directions, thereby enabling the LCD employing the backlight module to produce sufficient brightness.
Stacking of the first and second light converging sheets, and optical interference caused by optical sheets of the backlight modules result in Newton-rings. Since the upper diffusion sheet is configured to diffuse light and to induce haze effect, Newton-rings can be shielded and prevented from being observed on the LCD. Consequently, the LCD is able to have a good picture quality and a fine visual effect.
Another conventional backlight module may include only one light converging sheet. However, Newton-rings may be still produced when the single light converging sheet and other optical sheets of the backlight module are stacked one on top of the other. As such, smooth surfaces of regular micro-prism structures of the light converging sheet may give rise to rainbows. Therefore, a diffusion sheet is required to shield Newton-rings and the rainbows.
Amount of optical sheets of a backlight module can be reduced so as to lower production costs. For instance, the upper diffusion sheet of the conventional backlight modules can be eliminated to reduce a production cost of the LCD. Nevertheless, optical flaws such as Newton-rings are more easily observed, thereby adversely affecting the picture quality of the LCD.
Simultaneously reducing a production cost of an LCD and maintaining a picture quality of the same is hence an important goal. In order to reach the aforementioned goal, the conventional light converging sheets may be modified by varying the micro-prism structure thereof, or by disposing diffusion elements thereon (e.g., by applying diffusion coatings onto the back of the conventional light converging sheets).
When the upper diffusion sheet of the conventional backlight modules is removed, and when a peak-to-peak distance between adjacent ones of the micro-prism structures of the upper one of the first and second light converging sheets resides in an appropriate range, the first and second light converging sheets tend to generate less or even no Newton-rings. Furthermore, the modification of the micro-prism structures of the first and second light converging sheets can assist in reducing the amount of Newton-rings and alleviate effects of the rainbows. The inventors are unaware of previous studies directed to the effects of regulating the peak-to-peak distance between the adjacent ones of the micro-prism structures on Newton-rings and rainbows.